Computer-aided techniques are increasingly being used to validate the authenticity of security documents. Examples of security documents include passports, credit cards, ID cards, driver's licenses, birth certificates, commercial paper and financial documents. In some cases, security images are printed on, embossed in, engraved in, or affixed to the security documents to aid detection of counterfeiting or use of unauthorized documents generally. That is, the security images can include one or more security features, such as ultraviolet ink, retroreflective 3M Confirm™ images, and retroreflective virtual images that are difficult to reproduce and, therefore, lead to more reliable validation of the security documents and increased detection of unauthorized documents.